A broad research program on lipid-lipid and lipid-protein interactions is proposed. 1) Purified and delipidated cytochrome oxidase isolated from beef heart mitochondria will be reconstituted into bilayer membranes of well-defined lipid compositions for protein-lipid interaction studies. The structure of the metal sites in this protein, their spatial distribution and functional role in the overall process of electron transfer and oxygen reduction will be elucidated. 2) Similarly, band-3 protein from red blood cells will be reconstituted into lipid membranes of well-defined chemical composition. The state of aggregation of the intramembraneous particles in the reconstituted membranes will be visualized by freeze-fracture electron microscopy and the protein distributions thus derived will be correlated with the motional state of the bilayer membrane inferred from magnetic resonance experiments to provide insight on lipid-mediated protein-protein forces. 3) The interactions of chlorophyll a with glycolipids isolated from thylakoid membranes of chloroplasts will be investigated in model membranes to test a model under consideration for the structure of antenna chlorophyll. Chemical cross-linking will be developed for mapping structural proximity relationships between chlorophyll a and lipids in thylakoid membranes.